ADLINK Technology NuDAQ ACL-8454, Руководство пользователя

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12
•
Installation
(Default)
Figure 2.5 Jumper setting of CLOCK1
CLOCK2 (Low Frequency)
The clock source of CLOCK2 can be set by jumper ‘CLOCK2’. The
frequency could be 1 MHz or 100 KHz which are divided from
CLOCK1 . The CLOCK2 is provided for low frequency applications.
Figure 2.6 shows the jumper setting and the corresponding
frequency. The default setting of CLOCK2 is using 100 KHz.
1M
CLOCK2= 100 KHz
CLOCK2
100K
1M
CLOCK2= 1 MHz
CLOCK2
100K
(Default)
Figure 2.6 Jumper setting of CLOCK2
If user‘s application need a clock frequency lower than 100 KHz, the
first method is to use external clock source, the second method is to
use one counter to generate a frequency lower than 100 Khz then
cascaded the low frequency signal to the other counter’s clock
source. This
cascaded counter configuration is feasible on the ACL-
8454 by jumper setting. See the next section for details of h ow to set
cascaded counter.
2.8 Counters Architecture
There are at most four 8254 chips on the ACL-8454 card. The chip
#1 (U1) and chip #2 (U2) are default mounted on the card, therefore
6 counters are default on board. It is possible to expand to four 8254
chips by plugging the additional chip #3 (U3) and chip #4 (U4) into
ACL-8454 and totally 12 counters are available. The default counters
on chip #1 and #2 are labeled as counter #1 to counter #6. The
expandable counters on chip #3 and #4 are labeled as counter #7 to
counter #12. Some counters are default configured as
independent
counters and the others are default configured as cascaded
counters . Table 2.3 illustrates the relationship between the